In the past, when it was desired to obtain a printed copy of a computer output or output from data transmission devices, such as Teletypes, it was the practice to employ electromechanical printers. These printers typically have a replica of the character or symbol to be printed on a hammer which is struck against the paper with an inked ribbon between the character or symbol replica and the paper. The output may be printed one character or symbol at a time, as in a Teletype, or an entire line may be printed at once. In either case, the printing rate was severely limited by the inertia of the individual hammers. If the printing speed of such mechanical systems was increased, the complexity and cost of the resulting mechanism were also greatly increased. Magnetic printing systems had subsequently been developed wherein the character patterns to be printed were first magnetized upon a recording surface and a toner was applied to the surface where the particles of the toner were magnetizable and would adhere to the areas which had been previously magnetized.
Frequently it has been desired to use more than a single color for such types of printing. With the above-mentioned electro-mechanical printers, ribbons of different colors had to be provided and the ribbon shifted each time the color was to be changed. Such a requirement often precluded the use of color printing when a whole line of characters was printed at one time since it would be impractical to provide a separate ribbon for each character in the row of characters or to shift the ribbon separately as each separate character in the row was struck. An alternative was to print all the characters of a particular color at one time then to overlay that printing with a printing of all the characters of the second color. Registration problems were thus inherent between characters of different colors. In magnetographic printing systems, as in the present invention, it is not necessary to use a ribbon and hence not necessary to provide a mechanism for shifting that ribbon.